White cast iron



Patented July 25, 1950 s im STATES PATENT OFFICE 2,510,524 wnrra cas'rmoN Keith Dwight Hillis, Bahway, N. 1., assignor to The InternationalNickel Company, Inc., New York, N. Y., a corporation of Delaware NoDrawing.

The present invention relates to white cast irons, and, moreparticularly, to white cast irons having improved strength especiallywhen produced in the form of sand castings.

It is an object of the present invention to provide a white cast ironhaving an improved combination of mechanical and physical properties,particularly when produced in the sand cast condition.

It is a further object of the present invention to provide a white ironcasting having in the sand cast condition an improved combination ofhardness and transverse strength without sacrificing impact properties.

Other objects and advantages of the invention will be made apparent tothose skilled in the 4 art from the following description.

Broadly stated, the present invention contemplates a white cast ironcomposition containing about 2% to about 4.5% carbon, about 0.1% toabout 3% silicon, up to about 6% nickel, e. g., 0.01% to 6%, about 0.1%to about 2% manganese, about 0.015% to about 0.5% retained magnesium, upto about 2.5% chromium, e. 3., 0.

to 2.5%, up to about 2% molybdenum, e. g.,

taining about 3% carbon, about 0.75% silicon,

about 0.2% manganese and about 0.02% sulfur. A portion of the melt wascast without further additions. Two other portions of the same melt werecast after the incorporation of sufllcient magnesium to provide retainedmagnesium contents of 0.04% and 0.06%, respectively, in the finalsolidified products. The magnesium was introduced as anickel-magnesium-carbon alloy containing about 11.9% magnesium, 2.8%carbon and the'balance essentially all nickel. All three and impuritiesusually found in cast Application March 20, 1948, Serial N0. 16,139

5 Claims. (01. 75-123) cast irons were white cast irons in the as-castcondition, as evidenced by the white fracture exhibited by each of thecast irons. The three cast irons had the following properties:

e's roper es Pefi-ent ff HBrill 1300., Lead,

in. lbs

None 0. 088 4, 190 10 371 0.04 0.002 -0.sa0 375 l 1 1.2-inch dia.arbitration bar tested over 12-inch span.

The eflect of magnesium in improving the properties, particularly thetransverse breaking load, is further illustrated by the following datadetermined from a white cast iron containing about 3% carbon, about0.75% silicon, about 0.2% manganese, and about 0.015% sulfur and from acomparable white cast iron which contained, in addition, 0.13% retainedmagnesium:

Transverse Properties Percent Izod Impact,

8 it.-1bs. Dell, in. Load, lbs.

None 0.079 4, 580 i!) 0. l3 0. 091 5, 490 27 In order that those skilledin the art may have a better understanding of the invention, the

composition and propertiesof other illustrative white cast irons withinthe scope of the invention are set forth in Tables I and II,respectively. H

All the cast irons in these tables were sand cast and were tested in theas-cast condition.

TABLE I No Per Cent Per Cent Per Cent Per Cent Per Cent Per Cent O Si MnNi 5 Mg as 0.8 0.8 0.8 n. 0. 0. 024 2. 8 2. 1 0. 8 2. 0 U. 012 U. 064 3.4 1. 8 0. 8 2. 0 0. 016 0. 061 4. 1 l. 3 0. 5 1. 8 0. 02 0. 06

l n. d.-n0t determined.

TABLE III Many white cast irons containing about 0.75% to 2% nickel,about 2.5% to 3.3% carbon, about 0.5% to 296 silicon and over about0.04% retained magnesium have been tested and exhibited the followinghigh average properties when tested over a 12-inch span:

Transverse breaking load, 5,600 lbs. Transverse deflection, 0.102 in.

Within the aforementioned range of compositions, 9. special range ofcompositions has been discovered which have particularly outstandingproperties which render them especially useful for applications wherewear resistance, abrasion resistance and/or high hardness are desired.These compositions contain about 2.5% to 3.3% carbon, about 0.3% to1.25% silicon, about 3.5% to 5% nickel, about 0.4% to 0.9% manganese,and about 0.05% to 0.1% retained magnesium. The balance of thecomposition is essentially iron. White cast irons within this specialrange of compositions have improved properties as compared to similarwhite cast irons devoid of ma nesium but in which-some other element, e.g., chromium, is employed as a whitener. The improved propertiesexhibited by these special white east irons are particularly notable insand castings made therefrom. For certain applications, it may bedesirable to employ chill castings. white cast irons having theforegoing s ecial compositions will on the average exhibit propertieswithin the following ranges, the transverse load and deflection beingdetermined on 1.2-inch diameter sand cast arbitration bars tested over a12-inch span:

Load, lbs, 5000 to 6500 Deflection, in., 0.00 to 0.11 Izod impact.ft.-lbs., to Brinell Hardness No. 550 to 715 The aforementioned specialwhite cast irons are characterized by an unusual microstructure notfound in other white cast irons having the same nickel content butdevoid of magnesium. As is known to those skilled in the art, themicrostructure of analogous white cast irons usually will containmassive carbides arranged in a dendr itic or cellular pattern. In thespecial white cast irons of the invention, however, the microstructureis characterized by the presence of carbides in the form of laminationsor plates. A notable and unusual feature of the mlcrostructure i thediscontinuous nature of the carbide phase. The remainder or continuousportion of-the microstructure consists largely of martensite. Testsindicate that the unusual microstructure acabout 405 F.

TABLE III r- Pa- Per- Per- Per- Per- No. cent cent cent cent cent centOthers 0 Si 8 Ni Mn Mg 0.4 0.1! 4.5 0.4 0.07 0.4 0.!!! 4.5 0.4 0.07 0. 60. 02 4. 5 0. 5 0. 08 8 29 0.1 0.1 4.7 0.5 none 1 5 Cr 9 3.3 0.5 0.1 4.50.5 none 156:

TABLE IV No. Imd Dell. l Impact I BHN i Fracture 5 6,300 0.003 25 600White 6-- 5,2 0.077 2i 605 Do. 7- 5,85) 0189 20 586 Do. 8 4,881 0.105 285 D07 9 1 4,23) 0. 097 25 538 Do.

Lood=Tramverse load in pounds applied midwa between an ports to producefracture oi bar. y p .=Defled:i|n in inehm at maximum load in transversetest.

Impact=Izod impact value in foot pounds. BHN=Brindl hardness number. I4.5 Iii-1.5% Cr white iron such as sold under the trade-mark Ni- (Arm of9 boats counts substantially for the increased strength which has beenexhibited by the alloy of the invention.

An, unusual characteristic. of the aforementioned special martensiticwhite cast iron of the present invention is that the strength andtoughness' developed in the sand cast condition are as good. or, in manyinstances, are even better the chill cast condition. In this respect,the magnesium-containing martensitic white cast iron of the inventiondiil'ers markedly from the analogous magnesium-free white cast irons ofthe prior art since these prior art white cast irons are generallystronger, tougher and have a higher deflection in the transverse test inthe chill cast condition than in the sand cast condition. It has beenfound that the laminated or plate-like discontinuous carbide structuredescribed hereinbeiore and which is characteristic of themagnesium-eontaining martensitic white cast iron of the invention isparticularly well-defined or prominent when the martensitic white castiron of the invention is sand cast.

The term white cast iron" is used herein to mean a cast iron (1. e., aeutectiferous alloy of iron and carbon) which has an uncombined orgraphitic carbon content not more than about one-half the carbon contentin excess of that required to form the matrix, e. g., the eutectoidrequirement, and hasa white fracture.

In order that those skilled in the art may have a, better understandingof the properties exhibited by the special martensitic white cast ironsof the present invention, the compositions and propel-fies oimartensitic white cast irons within the contemplated range ofcompositions (Nos. 5, 6 and 7) together with compositions and propertiesof analogous magnesium-free white cast irons (Nos. 8 and 9), are givenin Tables In and IV. All the properties shown in Table III weredetermined on 1.2-inch diameter arbitiation bars cast in sand, except inthe case of Nos. 6 and 'I which were chill cast in iron molds. No. 6 hadthe same composition as No. 5 but diflered in that it was chill castwhereas No. 5 was sand cast. All the cast irons were subjected to atransverse test over 12-inch centers after a stress relief treatment JIii-1.5% Cr white iron such as sold under the trade-mark Ni-Hard."(Avaage or 15 beats.)

improved ability of the alloy of the invention to withstand transverseload. It has been found that when tested in the sand cast condition themarfor about 3 hours at tensitic white cast irons of the invention canwithstand a transverse load approximately to 35% greater than can bewithstood by an analogous magnesium-free white cast iron containingabout 1.5% of chromium as a whitening agent.

As is known'to those skilled in the art; the" foundry methods commonlyemployed to determine the chilling propensity of a given cast iron arethe chill block and the step 'bar. Table V contains the results of testsconducted on chill blocks to show the powerful whitening efieotconferred by magnesium in the martensitic white cast iron of theinvention. The chill blocks em-' ployed had dimensions of 6"x6"x2" withthe chill'being applied on the 6"x2" face and with the remaining facesof the block being cast against sand. In conducting the tests, the meltsemployed to produce the chill blocks were superheated to 2850*, F. andwere cast at 2500 F. The solidified blocks were broken in half in adirection perpendicular to the chill face. and were then examined fordepth of chill. The results are illustrated by the data in Table V.

A sand cast step bar having the composition of the aforementioned whitecast iron containing 0.13% magnesium was completely white in the largestsection of a step bar (the two-inch section) after being superheated toa temperature of 2850 F. and being cast at a temperature of 2650 F. '1

A beneficial eflect which has been found to accompany additions ofmagnesium to the molten cast iron compositions contemplated by theinvention is that magnesium has a very powerful I desulfurizing effect.It has been found that the reduction in sulfur content which takes placewhen magnesium is introduced into the molten cast iron consumes a partOf the magnesium introduced. Accordingly, when it is desired to.

introduce the amounts of retained magnesium contemplated by the presentinvention, it is first necessary to introduce a sufficient amount ofmagnesium to remove a major part of the sulfur present and to reduce thesulfur content of the white cast ironto alowvalue. When0.03 or moreretained magnesium is introduced into sulfurcontaining cast irons, thesulfur content will be reduced to about 0.02% or even less (e.g.,0.015%)However, if amounts of retained magnesium less than about 0.03% areintroduced, the sulfur level in the resulting solidified cast iron maybe higher, for example, 0.08%, depending upon the sulfur content of theiron before the introduction of magnesium. The final sulfur will varyinversely with the amount of retained magnesium. In

addition to the amount of magnesium required for sulfur removal, asuificient excess amount of magnesium must be introduced to provide therequired retained amounts of magnesium in the finalcasting. As anempirical approximation, it has been found that of the magnesiumactually introduced into the molten cast iron bath one part by weight ofmagnesium is consumed for each part by weight of sulfur which is removedfrom the bath. It has been found that this sulfur-removing property ishighly effective regardless of the conditions existing when magnesium isintroduced into the cast iron melt. Thus, no slag is necessary in orderto carry out a the removal of sulfur and the treatment is effecthen heldfor minutes and. at the end of this time, it was found that the sulfurcontent was 0.012% and the magnesium content was 0.015%. This loss ofmagnesium is characteristic of molten magnesium-containing cast ironsand is due to a number of factors including oxidation of the magnesium,boiling of! of the magnesium as vapor, etc. It can be said that about0.03% to about 0.06% magnesium is'lost in about ten min-.

utes when magnesium-containing molten cast iron is held in hand ladiessuch as are employed in the foundry.

In all instances where it is attempted to introduce magnesiuminto molteniron-base baths, it is important to bear in mind the high reactivity ofmagnesium and to exercise due precaution in order that reactions ofexplosive violence be avoided. It has been found that if it is attemptedto add magnesium to cast iron melts when the melts are at the ordinarycasting heat, reactions of explosive violence take place which willpropel the molten metal from the receptacle in which it is contained andresult in loss of both molten metal and magnesium without introductionof magnesium into the melt. It has been found that metallic magnesium inthe amounts contemplated by the present invention could be introduceddirectly into cast iron melts when the latter are in a pasty conditionat a temperature only slightly above the melting point. When this methodis employed, it is then advisable after .the magnesium introduction toraise the temperature of the bath quickly to a suitable castingtemperature in order that sound castings be obtained. A method which hasbeen found satisfactory for the purpose of introducing magnesium intothe cast iron melts is to first alloy the magnesium with a metalliccomposition which is soluble in the molten iron to be treated and inwhich the magnesiumis, in turn, soluble. Satisfactory addition agentsare nickel or copper alloys containing up to about 20% of magnesium, e.g., a nickel alloy containing 4% to 20% of magnesium. It is to bepointed out that even in these alloys, the high reactivity of magnesiumis still felt. In fact, alloys containing 10% magnesium have been foundto burn brightly when placed on top of the molten metal. Recovery ofmagnesium from the addition agents in terms of magnesium actuallyretained in the solidified iron casting will vary depending upon thecon- .centration of magnesium in the alloy, the temperature of the bathto which the magnesium is added, the composition of the bath, includingthe nickel and sulfur contents thereof, etc. Generally speaking, therecoveries of magnesium are rather low; for example, in one instancewhere -vention 0.5% maanesium was added in Uniform or a nickel alloycontainin: 20% .of magnesium to a cast iron melt containing 0.05% ofsuliur, 0.13% or um was actually recovered in the solidified casting-The maanesium-containin: alloy of the inn a an unusual combination ofproperties, since the transverse strenzth and denection thereof areimproved above that or analogous magnesium-tree alloys without anysacrifice of impact or hardness. Because 01 this unusual combination ofproperties, the magnesiumcontaining white cast iron the invention findsapplication in a wide number of fields in which the high hardness, wearresistance, abrasion resistance and moderate toughnes of this materialmay be beneficially employed; For example,

grinding balls, attrition mill plates, rolls, pump parts, miningmachinery parts, mullet tires, nozzles, etc., can be made iromthe whitecast iron oi the present invention. l

Although the present invention has been de- I scribed in conjunctionwith preferred embodiments, it is understood that modifications andvariations may be resorted to without departing from the spirit andscope oi the invention, as those skilled in the art will readilyunderstand. Variations and modifications apparent to thou skilled in theart are considered to be within the purview and scope of the inventionand appended claims.

I claim:

1. A. casting comprisedoi' a white cast iron containing about 2.5% to3.3% carbon, about 0.5% to 2% silicon, about 0.75% to 2% nickel, about0.04% to 0.5% mum. less than about 0.020% sulfur and the balanceessentially iron.

2. A casting comprised or a white cast iron containing about 2% to 4.5%carbon, about 0.1% to 3% silicon, about 0.1% to about 2% manganese,about 0.01% to 6% nickel, about 0.01%

. 8 2.5% chromium, about 0.01% to about 2% molybdenum, about 0.03% toabout 0.5% maznesium, less than about 0.020% suliur'and the balanceessentially iron.

8. A casting comprised oi a white cast iron containing about 2.5% to3.3% carbon, about 0.3% to 1.25% silicon, about 3.5% to 5% nickel, about0.4% to- 0.9% manganese, not more than about 0.02% sulfur, about 005% to0.1% magnesium, and the balance essentially iron.

4. A casting comprised 01 a white cast iron containing about 2% to 4.5%carbon, about 0.1% to 3% silicon, about 0.1% to 2% maganese, about 0.03%to about 0.5% magnesium, less than about 0.020% sulfur and the balancessentially iron.

5. A casting comprised. of a white cast iron containing about 2% to 4.5%carbon, about 0.1%

to 3% silicon, up to about 0% nickel, about 0.1%

to 2% manganese, up to about 2.5% chromium, up to about 2% molybdenum,about 0.03% to 0.5% magnesium, less-than about 0.02% sulfur and thebalance essentially iron.

I KEITH DWIGHT MIL-LIB.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. A CASTING COMPRISED OF A WHITE CAST IRON CONTAINING ABOUT 2.5% TO3.3% CARBON, ABOUT 0.5% TO 2% SILICON, ABOUT 0.75% TO 2% NICKEL, ABOUT0.04% TO 0.5% MAGNESIUM, LESS THAN ABOUT 0.020% SULFUR AND THE BALANCEESSENTIALLY IRON.